Made a few custom boards to test different deck shapes. My personal experience, definitely no convex under the feet. A little concave on front or back can be nice, too much hated it. I am now riding perfectly flat decks front and back foot.

I had flat, now i have concave front an rear. Its like a skateboard deck in the fact that a bit of concave helps lock your feet a bit, but it also make the board stiffer and more responsive to input. Makes for a more lively ride that flat board. You make like it or not like it. Certainly makes the flying foot switch hard as the board is more twitchy.